Fertile Store Bought

On the weekend I found the white dot on the yolk of store-bought eggs.
I opened 8 and 7 had the dots.
Some of my own fertile eggs have that when I bring them in from under the broody.
If I left them another day that dot would be a bullseye.
Right?

Hm, were those store bought eggs marked FERTILE? The bullseye is there from the start, right when you crack open the egg. A white dot means INfertile. I've never seen fertile eggs in a supermarket myself.